PPRuNe Forums - View Single Post - Helicopter Dynamics: Gyroscopic Precession
Old 15th Mar 2014, 23:47
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AnFI
 
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Feeling sorry for blain:
Originally Posted by [email protected]
AnFI, read awblains comment about max pitch being the point of max lift and you will see he is wrong and that is why I emphasised the AoA (which is max at the same point as max rate of pitch change) as being the main issue.
I am not so sure you are right; we are talking about a disk with no airspeed, i presume, to isolate the effect we are discussing. Where the AoA is highest to cause a Rate of Attitude Change is surely where the Flapping Rate (ref'd against Mast Axis or previous TPP) is highest ie where the inertial path of the blade needs to be altered to achieve a new plane of rotation, this is (approximately) the same place in the cycle as the delta-Pitch (amount, not rate) is the greatest. This is approximately at 90deg to the place where we want the blade to have flapped up (or down). Or to use your terms (which are good) the blade is flown from low to high by the extra AoA, achieved by extra pitch. tbf i might be wrong (am I?) about this tho, without deeper thought. (so I don't think he is as wrong as you make out)

(and also; Max Rate of Pitch Change is 90deg before (and after) Max Pitch. IE at the Front (and Back) for an Attitude Change in the Pitching direction)

Yup it's great to see us (almost all) move away from Gyroscopic precession, which i think was achieved courtesy of pprune discussion rather than CFS?

Of course (as blain (rightly) says) these are not incompatible theories, there is still an inertial phenomenon (angular momentum) that needs to be accounted for. It's just that the angular momentum is not (mostly) (rigidly) coupled to the rotor mast (as the De Cierva reference makes clear). So a damped resonant free flapping wing becomes the elegant way to think about the blade, as you say. (finding hairs on eggs)
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